Look, the priority system combines linear (points) and progressive (karma) methods. If people don't follow the established order of actions during the character creation then they will get different results, potentially giving someone an unfair advantage or a disadvantage over others. That difference has nothing to do with optimisation or minmaxing. 2+2*2 equals 6 if you follow the order, or 8 if you don't.
There's an example: person A picks priority C for metatype that gives him an Elf with 3 SAPs. Person A then proseeds to spend the SAPs to raise Edge to 4 and spends 25 karma to get Edge 5. Meanwhile, person B spends 25 karma to raise edge 1->3, and after that applies an Elf 3 pattern, giving her Edge 6.
Person B has an advantage not because they are being smart about building a character but due to ignoring the build order.
Steps 1 to 8 provide a uniform pattern for players to start in uniform conditions. You wouldn't join a Street Scum campaign with a High Life Prime Runner character, right?